1. Field
This patent specification generally relates to a method and apparatus for a mobile phone, and, in particular, to a method and apparatus for a mobile phone capable of reproducing and/or recording audio using a semiconductor device which performs inter-processing of digital audio and voice signals to increase the quality thereof.
2. Discussion of the Background
The increase in packing density of large-scale integration (LSI) in recent years has promoted tighter packing of functions used in a mobile phone. Multi-functional mobile phones thus are now becoming common and are capable of working as a telephone and music player, or as a telephone, a music player, and a movie and music recorder at the same time, for example. Such a mobile phone uses an installed LSI component or a discrete component, as necessary, to mix a voice signal with an audio signal. The voice signal is input from an input device, such as a microphone, or received from another telephone and demodulated, while the audio signal is reproduced in the mobile phone. A signal mixed in such a manner is transmitted to an output device such as a speaker or a headphone.
FIG. 1 is a block diagram showing an exemplary unit for sound processing used in a conventional mobile phone, as described in Japanese Laid-Open Patent Application Publication No. 2000-299718, for example.
In FIG. 1, a received and demodulated digital voice signal SDVa is converted into an analog signal with a voice digital-to-analog (DA) converter 101, processed with a volume adjustment and so forth in an analog processing circuit 104, and output from a voice output device, such as a first speaker SP1. A reproduced audio signal SDA is converted into an analog signal with an audio DA converter 103. An analog processing circuit 106 performs on the converted audio signal SDA an addition or subtraction with the analog voice signal, or a volume adjusting. The processed audio signal SDA processed is then output from an audio output device such as a second speaker SP2 or a headphone HP.
An analog voice signal from a voice input device, such as a microphone MIC, on the other hand, is processed with an analog processing circuit 105 which performs a volume adjustment, an,addition/subtraction with the analog audio signal, or the like. The processed analog voice signal is further converted into a digital voice signal SDVb with an audio analog-to-digital (AD) converter, and transmitted to a processing block for a modulation and transmission. It is to be noted that a signal path of a mixed signal of voice and audio shown in FIG. 1 is one possible example. There may be various signal paths for the mixed signal, depending on a type of the mobile phones.
A conventional technique, however, experiences problems such as deterioration in quality of an analog signal or generation of auditory noise due to high-frequency noise in a mobile phone, caused by analog signal processing, that is, an addition/subtraction or a volume adjustment using an operational amplifier.
It is also desirable to provide a mobile phone using a semiconductor device which is capable of mounting a digital class-D amplifier in place of a class-AB amplifier, thereby increasing electric power efficiency.